The separation of the control level from the bearer level is a rather new feature in a core network of a mobile communication system. The separation is done by dividing the tasks of a Mobile Switching Center (MSC) between a Media Gateway (MGW) and a MSC Server (MSC-S). A MSC-S basically performs control tasks while a MGW acts as a translation unit between disparate telecommunications networks.
Control tasks of a MSC-S may comprise call control of all circuit-switched services, user plane control and media gateway control. Similar tasks may be performed by so-called Gateway MSC-S (GMSC-S) or Transit Switching Center Server (TSC-S). In order to ease the understanding, in the further parts of this application it will not be differentiated between MSC-S, GMSC-S, and TSC-S or the like but instead it will be referred to a generalized term “Switching Server” (SS).
Media Gateways enable voice and/or multimedia communications over multiple transport protocols such as Asynchronous Transfer Mode (ATM) and Internet Protocol (IP). A MGW is the termination point for external networks and the interface between the core network and the radio network. It terminates circuits and packet streams and may support media conversion, bearer control and payload processing.
For a call, a bearer has to be established along the communication path between the calling and the called party. Tasks of a SS are the selection of a MGW and of bearer characteristics like codecs for bearer segments interfacing the selected MGW. Typically, the selection of the MGW and the codec happen in parallel. Tasks of a (selected) MGW are to establish at least one bearer segment according to the selected bearer characteristics. Furthermore, a MGW may perform media conversion, bearer control, and payload processing.
Either “forward bearer establishment” or “backward bearer establishment” may be used as specified in 3rd Generation Partnership Project Technical Specification (3GPP TS) 23.205 V.7.2.0 (2006-06). “Forward bearer establishment” is also known as “deferred MGW selection” and “backward bearer establishment” is also denoted as “non-deferred” or “immediate MGW selection”, because a main differentiating feature between the two bearer establishment procedures relates to timing and responsibility of a first selection of a MGW for a call. According to backward bearer establishment, the originating SS performs a first MGW selection and subsequently the terminating SS performs a second MGW-selection and vice versa for forward bearer establishment.
For forward bearer establishment, the originating SS is provided with information about the MGW-selection already performed by the terminating SS. Furthermore, the originating SS is provided with bearer information (information about bearer characteristics) from the terminating side. Accordingly, the originating SS can take MGW-selection information and bearer information from the terminating side already into account when performing MGW-selection at the originating side for establishing the bearer in an optimized way. According to backward bearer establishment, the SS at the terminating side is not provided with such information from prior MGW-selection and not with bearer information from the originating side.
Forward and backward bearer establishment are further explained in more detail with reference to FIG. 1 for a call originating from a terminal T1 on an originating side to a terminal T2 on a terminating side. Furthermore, depicted are switching servers SS-1,SS-2 and media gateways MGW-1,MGW-2 on the respective originating and terminating side as well as network N1 on the originating side and network N2 on the terminating side. Networks N1,N2 are usually networks with different transmission characteristics, e.g. network N1 may be a Radio Access Network and network N2 may be a Public Switched Telecommunications Network (PSTN), Integrated Service Digital Network (ISDN), or a further Public Land Mobile Network (PLMN network), and one or more media gateways MGW-1,MGW-2 are needed to establish the bearer end-to-end adapted to the capabilities of the interfacing links, networks, and devices. Hence, bearers segments B11,B12,B13 may have to be established to accomplish for a bearer for the call. The communication system 100 may comprise further entities not depicted for illustrative reasons, e.g. a Home Location Register (HLR).
According to backward bearer establishment for a call to terminal T2 originating at terminal T1, a first MGW selection is performed as soon as a request for a call is made at switching server SS-1, which selects media gateway MGW-1. According to forward bearer establishment, switching server SS-1 does not select any MGW but forwards an Initial Address Message to switching server SS-2 which selects media gateway MGW-2 according to first MGW selection. Subsequently, the respective second MGW selection can take place, i.e. media gateway MGW-2 is selected by switching server SS-2 for backward bearer establishment and media gateway MGW-1 or media gateway MGW-2 is selected by switching server SS-1 for forward bearer establishment, and the bearer can be set-up along bearer segments B11,B12,B13 as described for mobile originating and mobile terminating examples in 3GPP TS 23.205 V.7.2.0 (2006-06) herewith included by reference.
A resource efficient arrangement of a communication network 100 is depicted in FIG. 2 wherein a bearer for a call to terminal T2 originating at terminal T1 has been established according to forward bearer establishment. Switching server SS-1 has received information about the previous selection of the MGW on the terminating side and has selected the same media gateway MGW-2 as previously been selected by the switching server SS-2. Accordingly, a reduced number of media gateways and bearer segments are used compared to FIG. 1.
An inherent feature of the Intelligent Network (IN) concept is that service intelligence is separated from switching functions. This separation basically enables network operators to develop and deploy services and features independently of vendors, allowing more flexibility in service development, simplified rollout, reduced costs and greater autonomy. Examples for IN are the Intelligent Network Application Protocol (INAP), the Advanced IN (AIN), and the Customized Applications for Mobile network Enhanced Logic (CAMEL). INAP was developed for fixed line networks and is the primary protocol used for fixed line IN outside of North America. AIN is a variant developed for North America.
CAMEL is a Global System for Mobile Communications (GSM) Phase 2+ and Wideband Code Division Multiple Access (WCDMA) network feature standardized according to 3GPP TS 22.078. CAMEL is based upon core INAP with modifications to take into account subscriber mobility. In particular, CAMEL enables the use of operator-specific services by a subscriber even when roaming outside the subscriber's Home Public Land Mobile Network (PLMN). A CAMEL-IN comprises as main entities a gsmSSF (GSM Service Switching Function) for switching tasks and a gsmSCF (GSM Service Control Function) comprising the service intelligence or logic.
The layered architecture and the IN are fairly separate concepts. In general, however, establishing a bearer for a call independently from the IN service logic can be problematic. For example, some IN services may be provided only, or at a better quality, for particular bearer establishment procedures or bearers only.
Furthermore, especially for multiparty calls like conferencing, individual bearer segments may be incompatible because of incompatible or not connectable MGWs and/or incompatible codecs. Drawbacks apply for the so-called “automatic backward selection feature”. The automatic backward selection feature can be installed at a gsmSSF and forces the gsmSSF for any call to always initiate backward bearer establishment which is not appropriate for many calls.